I'm on a 64 bit platform. So the first thing I do is set JDev to use 64bit JDK by editing the jdev.conf file i.e.
...
# Directive SetJavaHome is not required by default, except for the base
# install, since the launcher will determine the JAVA_HOME. On Windows
# it looks in ..\..\jdk, on UNIX it first looks in ../../jdk. If no JDK
# is found there, it looks in the PATH.
#
#SetJavaHome D:\Oracle\Jdev\111230-prod\jdk160_24
SetJavaHome C:\Program Files\Java\jdk1.6.0_39
...

I'll also add the parameters for JDBC driver and path to the OCI dll's.